Generally, a motor is operated at a high speed and a low torsion force. In other words, it is difficult to drive a large-sized load. Consequently, for allowing the motor to drive a heavy object, a speed reducer is used for reducing the rotating speed of the motor and increasing the torsion force.
Conventionally, the speed reducers are classified into several types, including rotary vector (RV) reducers, harmonic drive reducers and cycloid speed reducers. For example, the RV-E series reducer is a two-stage speed reducer produced by Nabtesco. The RV-E series reducer comprises a first speed reduction stage with a spur gear and a second speed reduction stage with an epicyclic gear. The gears of the first speed reduction stage and the second speed reduction stage are made of metallic material. The RV-E series reducer is a two-stage reduction design to reduce vibration and inertia while increasing ratio capabilities. The RV-E series reducer provides high-end performance in highly rigidity and high reduction ratio configurations, and the rolling contact elements of the RV-E series reducer have high efficiency and long life. However, since the RV-E series reducer has larger volume and weight and has many components, the cost of the RV-E series reducer is high.
The harmonic drive reducer comprises a wave generator, a flex gear and a rigid gear. The elastic deformation of the flexible gear can be controlled to result in a pushing action so as to transmit motion and power of mechanical transmission. The harmonic drive reducer has smaller size, lighter weight and higher precision when compared with the RV reducer. However, since the rigidity of the flex gear of the harmonic drive reducer is low, the harmonic drive reducer is unable to withstand high impact and has a problem of causing teeth difference friction. In other words, the use life of the harmonic drive reducer is shorter. Moreover, since the input speed of the harmonic drive reducer is not high, the reduction ratio of the harmonic drive reducer is lower.
Conventionally, a cycloid speed reducer comprises an eccentric shaft and two cycloid discs. Each of the two cycloid discs comprises at least one tooth. Moreover, the two cycloid discs are linked with a power input shaft and a power output shaft, respectively. During operations of the cycloid speed reducer, one cycloid disc is rotated with the power input shaft through the eccentric shaft, and the power output shaft is rotated with the other cycloid disc. Through the corresponding tooth structures, the two cycloid discs are correspondingly rotated. The conventional cycloid speed reducer has many benefits such as high transmission ratio, compact structure and high transmission efficiency. However, in case that the conventional cycloid speed reducer is applied to a high-load circumstance, the two cycloid discs of the conventional cycloid speed reducer have to withstand high load. If the cycloid discs have insufficient structural strength, the cycloid discs are possibly damaged and thus the cycloid speed reducer is abnormal. Moreover, because of the eccentric shaft, the rotation of the conventional cycloid speed reducer is deflected in a specified direction. For compensating the dynamic equilibrium, the conventional cycloid speed reducer is additionally equipped with a weight compensation device. If the dynamic equilibrium is not effectively compensated, the conventional cycloid speed reducer generates obvious vibration.
Therefore, there is a need of providing a cycloid speed reducer with the characteristics of a RV reducer and a harmonic drive reducer and capable of achieving high reduction ratio, high rigidness and dynamic equilibrium in order to the overcome the above drawbacks.